After the iPad has enrolled MDM via DEP, you can mark it as Shared iPad in order to use Managed Apple ID.
- Check if the device has installed MDM/Remote Management via DEP
Apple > DEP > DEP Device
- Set as Shared iPad
Action > Set Shared iPad
- Wipe Device and re-enroll the device as Shared iPad
Device > Device Management > Select the device with Shared iPad label > Advanced > Wipe Device